A phase-locked loop functions as a feedback control loop that detects a reference frequency signal, and generates and outputs a signal with a frequency and phase related to an input reference frequency signal. The negative feedback maintains the output signal locked to the reference signal, or, acts to bring the output signal into the same frequency and phase as the reference signal and then locks the output to the reference signal. The many applications of a phase-locked loop include stabilizing a signal, generating an analog signal with the same frequency as the input signal, signal demodulation, and the detection of a signal in the presence of noise.
Phase-locked loops are widely used in radio, telecommunications, computers, and a large range of other electronics systems. However, one limitation of phase-locked loops is the tendency for each component to exhibit drift when the phase-locked loop experiences temperature change, frequency level changes, changes in power, or other environmental shifts. The effect of drift in the components of the circuit, if the drift becomes significantly large, may be to jointly offset the average frequency of the oscillator in the phase-locked loop to the extent that it becomes difficult for the loop to become, or remain, locked to the reference frequency.
Solutions to this problem have been described in the prior art, including inversing the temperature drifts of the blocks of the circuit, introducing the desired offset voltage to the circuit, and inverting the DC into an AC phase difference. These solutions are limited by practical factors, such as the difficulty of matching inverse temperature drifts of the circuit blocks, and by cost factors, such as the cost of inverting DC into AC phase difference.
Accordingly, there is a need for a phase-locked loop that can adapt to extreme temperature, frequency, and power changes, as well as other environmental changes, while remaining able to in maintain, or achieve, a locked state with a reference frequency.